In-Situ Phosphatizing Coatings III: A Water-Reducible Alkyd Baking Enamel

By Tao Yu, Chhiu-Tsu Lin

We report the successful formulation of stable and compatible in-situ phosphatizing coatings (ISPCs) for a waterborne alkyd-amino baking enamel applied on bare cold-rolled steel (CRS), iron phosphated Bonderite 1000 (BD), and iron phosphated plus Parcolene 60 chromated (BD+P60) coupons.

The enhanced coating adhesion of water-based ISPCs is confirmed by the cathodic delamination measurements. After 100 hr of salt spray (fog) test, the corrosion resistance performance (measured by the corrosion disbondment across the “X” scribe, d in mm) of the water-based ISPC on CRS panel (d = 4.0-7.0 mm) outperformed that of the control alkyd paint on B-1000 (d = 26 mm) and also on BD+P60 (d = 14 mm) coupons.

The superior coating performance of water-based ISPCs is believed to result from the in-situ metal surface phosphatization as detected by the reflectance FTIR technique.